Process-dependent defects in Si∕HfO2∕Mo gate oxide heterostructures

The authors have used low energy electron-excited nanoscale-depth-resolved spectroscopy to probe the bulk and interface defect states of ultrathin Mo∕HfO2∕Si with conventional process sequences. Multiple deep level emissions are evident below the 5.9eV HfO2 near band edge, including three associated with HfO2 oxygen vacancies in different charge states predicted theoretically. Defects resembling SiO2-related nonbonding oxygen hole centers and positively charged O vacancies increase with depth within the 4nm HfO2 film suggesting Hf silicate formation at the HfO2∕Si interface. These states vary dramatically between process sequences and can be understood in terms of known reactions at HfO2–Si interfaces.